1. Field of the Invention
The present invention relates generally to wireless communication systems, and particularly to wireless picocellular communication systems and radio-frequency identification (RFID) systems.
2. Technical Background
Wireless communication is rapidly growing, with ever-increasing demands for high-speed mobile data communication. As an example, so-called “wireless fidelity” or “WiFi” systems and wireless local area networks (WLANs) are being deployed in many different types of areas (coffee shops, airports, libraries, etc.). Wireless communication systems communicate with wireless devices called “clients,” which must reside within the wireless range or “cell coverage area” in order to communicate with the access point device.
Wireless Picocellular Systems
One approach to deploying a wireless communication system involves the use of “picocells,” which are radio-frequency (RF) coverage areas having a radius in the range from about a few meters up to about 20 meters. Because the picocell covers a small area, there are typically only few users (clients) per picocell. This allows for minimizing the amount of RF bandwidth shared among the wireless system users. Also, picocells allow for selective wireless coverage in small regions that otherwise would have poor signal strength when covered by larger cells created by conventional base stations.
Picocells are created by and centered around a wireless access point device that includes an RF transmitter/receiver operably connected to an antenna. The size of a given picocell is determined by the amount of RF power transmitted by the access point device, the receiver sensitivity, antenna gain and the RF environment, as well as by the RF transmitter/receiver sensitivity of the wireless client device. Client devices usually have a fixed RF receive sensitivity, so that the above-mentioned properties of the access point device determine the picocell size.
Combining a number of access point devices creates an array of picocells that cover an area called a “picocellular coverage area.” A closely packed picocellular array provides high-data-throughput over the picocellular coverage area.
Radio-Frequency Identification
Radio-frequency identification (RFID) is a remote recognition technique that utilizes RFID tags having information stored therein. The stored information is retrievable via RF communication between the RFID tag and an RFID tag reader. The typical RFID system utilizes an RFID reader (e.g., hand-held) that when brought sufficiently close to an RFID tag is able to read an RFID tag signal emitted by the tag. RFID systems are used for inventory management and product tracking in a variety of different industries, as well as in libraries and hospitals.
There are three main types of RFID tags. The first type is a passive RFID tag that has a microcircuit (typically, a digital memory chip) with no internal power supply. A passive RFID tag is powered by an incoming RF signal from the RFID tag reader. The RF signal provides enough power for the microcircuit to transmit the information stored in the RFID tag to the RFID reader via an electromagnetic RF tag signal.
The second type of RFID tag is semi-passive, and includes a microchip plus a small power supply so that RFID tag can generate a stronger RF tag signal, leading to a greater read range. The third type of RFID tag is active and, like the semi-passive type tag, has its own power supply. Active RFID tags generate an outgoing RF tag signal and can respond to RF signal queries from the RF tag reader, or periodically generate their own outgoing RF tag signal.
Implementing an RFID system that covers a relatively large area (e.g., an entire office building) and that track many items with high-resolution usually requires deploying a large number of RFID tag readers and connecting them to a central computer that can process the data received from the RFID tags. Reading the RFID tags is accomplished, for example, by people physically carrying RFID tag readers over the premises and interrogating each RFID tag. This conventional approach to RFID is equipment-intensive and labor-intensive, and tends to be expensive to implement and maintain.